Device for determining the shearing strength of the bordering layer of sand molds and cores



y 1966 F. SZATMARI ETAL 3,248,926

DEVICE FOR DETERMINING THE SHEARING STRENGTH OF THE BORDERING LAYER OF SAND MOLDS AND CORES Filed Dec. 2, 1963 2 Sheets-Sheet 1 Fig. I

INVENTOR 5 Fe rene S2 almarv F'Fanz as y 3, 1966 F. SZATMARI ETAL 3,248,926

DEVICE FOR DETERMINING THE SHEARING STRENGTH OF THE BORDERING LAYER OF SAND MOLDS AND CORES Filed Dec. 2, 1963 2 Sheets-Sheet 2 Fig.3

INVENTOR S I a 1'! United States Patent 3,248,926 DEVICE FUR DETERMINING THE SHEARING STRENGTH OF THE BORDERING LAYER 0F SAND MOLDS AND CORES Ferenc Szatmari and Franz Kern, both of Sehaffhausen,

Switzerland, assignors to George Fischer Aktiengesellschaft, Schalfhausen, Switzerland Filed Dec. 2, 1963, Ser. No. 327,341 Claims priority, application Switzerland, Dec. 7, 1962, 14,452/62 3 Claims. (til. 73-154) The present invention relates to a method of and device for determining the strength of the bordering layer below the surface of unilaterally highly heated compacted foundry or molding sand. When casting in sand molds, the sand and core surfaces of the mold and core wall are very quickly heated by direct contact with liquid metal or by heat radiation therefrom. In view of the poor heat conductivity below the heated sand surface, a strong temperature drop occurs, as a result of which above a cooler base, a highly heated crust or skin of a few millimeters thickness is formed. In the highly heated zone of this skin, due to the well-known strong expansion of quartz sand, correspondingly strong pressure stresses occur, whereas such stresses do not occur in the colder sand areas of the mold. The sand crust or skin borders the colder zone or area along a sharply defined border line. If the pressure stress in the sand skin is high while the sand strength in the border layer is low, it may occur that the sand skin will detach itself along the said border layer. As a result thereof, on the surface of the finished cast work piece, a more or less highly noticeable phenomena of detachment of the crust or sand skin, will be noted. These phenomena appear as surface irregularities in the form of depressions, elevations, grooves and the like. These phenomena appear with wet cast clay bound sand molds as well as with the dry clay bound sand molds and with organic or otherwise bound molds and cores.

These phenomena can be properly tested and investigated only when the sand skin, as is the case with molds used in actual operation, is heated above the conversion temperature from beta-alpha quartz, i.e. in excess of 1067 F. as is the case, for instance, in sand molds in which the metals are cast at a minimum temperature of about 1292 F. Also important in this connection is the speed at which the expansion forces develop and the magnitude of said expansion forces as well as the magnitude of the border layer strength between the sand skin and the border layer of sand therebelow.

Testing methods are known by means of which the skin formations on unilaterally surface highly heated and compacted foundry molding sands and core sands are ascertained purely visually. These methods, however, do not permit any investigation concerning the determination of the shearing strength at temperatures of operation in the border layer between the highly heated sand skin and the still relatively cool sand therebelow. There has also be come known a high temperature testing apparatus which, however, is used exclusively for the ascertainment of the expansion behavior and the strength of foundry molding sands.

It is, therefore, an object of the present invention to provide a method and an apparatus which will make it possible, in a simple manner, to determine the shearing strength in the border layer when a sand skin is formed.

It has been found, according to the present invention,

Patented May 3, 1966 that with the formation and detachment of sand skins referred to above under the influence of a sudden heating, by contact with the cast metal or by heat radiation, the border layer below the sand skin or crust is, by the pressure stresses occurring in said sand skin, subjected primarily to shearing stresses. Based on this finding, it is a further object of this invention to provide a method and device which will make it possible to ascertain the said shearing strength as a function of the heating time and the heating temperature respectively.

The knowledge of the magnitude of this shearing strength is of great importance in order to be able to predict the inclination or tendency of compacted wet and dry cast forms and cores to result in faulty casting. With wet casting, the test body is tested directly after the compacting, i.e. in still moist condition, whereas with dry casting and core sands, the test body is tested after corresponding drying, baking and other hardening procedures.

The above-mentioned objects and other objects and advantages of the present invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIGURE 1 illustrates the forming of a test body according to the present invention on a compacting device;

FIGURE 2 shows an enlarged section of the testing body;

FIGURE 3 illustrates partly in side view and partly in section a shearing strength testing device and the testing body, as well as a heating source arranged above the testing body and in operative condition;

FIGURE 4 is a top view of FIGURE 3 with the heating source moved out of alignment with the testing body.

The problem underlying the present invention has been solved according to the present invention in that first a test bodyprovided at one end with two rings arranged one upon the otheris manufactured in a manner known per se and disclosed, for instance, in German Industrial Standards DIN 52401. By varying the number of impacts, any desired compact as it may occur in practice can be produced in the mold or core. In this connection it is to be noted that the cylindrical inner surfaces of the two rings are provided with a rough surface in order to prevent any accidental slipping of the rings from the testing body.

For carrying out the shearing strength test, the test body inserted into the hollow cylinder is placed on a support of the shearing stress testing apparatus. This apparatus is composed primarily of three functionally cooperating structural units arranged on a common bottom plate. These three units are: a heating source, a hydraulically operable shearing strength testing device, and a support for receiving the test body. In conformity with the conditions prevailing in molds having received the cast metal, the test body is, by means of a heating source, heated quickly and to a high temperature, and subsequently is immediately subjected to a testing operation by the shearing strength testing apparatus, the ring arranged at the upper end of the testing body being sheared off from the test body. The thickness of the ring being sheared off from the test body corresponds approximately to the thickness of a sand skin as it forms in sand forms and cores under the influence of the casting heat.

For carrying out the method according to the present invention, first with a tamping 0r compacting device of any standard type, there is prepared a test body from J) foundry sand, the volume, weight and composition of said test body being predetermined.

The device shown in the drawing comprises a base 1 having connected thereto a bottom plate 2 with recesses 3 and 4 (see FIG. 2) for receiving a hollow cylinder 9 and two rings 6 and 5. Between ring 6 and hollow cylinder 9 there is provided a slight distance in order to make sure that ring 6, during the shearing test, will not rest against the edge of hollow cylinder 9. Ring 5, resting on ring 6 will, during the shearing test, eliminate the frictional resistance which otherwise, if ring 5 were not provided, would have to be overcome by the sand adhering to one side of ring 6. Rings 5 and 6 are mounted on surface 8 of bottom plate 2, and a predetermined quantity of foundry sand was poured into the inner chamber for producing the test body 11, said inner chamber being confined by surface 8, the recesses for rings 5 and 6, and the inner wall of the hollow cylinder 9. By means of the driver or compacting piston 10, in a manner known per se, three driving strokes are carried out for compacting the loose sand. When the compacting piston 10 occupies its upper position, the hollow cylinder 9 together with the now completed test body 11 and with rings 5 and 6 is lifted out of the recesses 3 and 4 of the bottom plate 2, and for further processing is placed with its upper side upon a support 13 firmly connected to a bottom plate 12 (FIG. 3). For purposes of connecting the hollow cylinder 9 there is provided a short cylindrical body 14 forming a unit with the support 13. On one side of the body 14 there is provided a groove-shaped recess 15 whereby, when slipping hollow cylinder 9 over the cylindrical body 14, the air will be allowed to escape from the chamber between the cylindrical body 14, the test body 11 and the inner wall of the hollow cylinder 9.

For further practicing the method according to the present invention, the test body 11 is, by means of a suitable heating source, heated up by heat radiation or by heat conduction. The heating unit consists of a base plate 40, a pipe 41 with an adjusting screw 42, a bar 43 vertically displaceable in pipe 41 and tiltable, and a heating body 44 which, provided with a heating plate 45, is suspended on an upper bent portion of bar 43. Expediently, the heating unit is connected to the bottom plate 12 by means of screws and is so placed that when tilting or moving in the heating body 44, the test body 11 will be completely covered by the heating plate 45. When heating up the test body 11, care has to be taken, in order to avoid heat loss, to the effect that the air gap between the test body 11 and the heating plate 45 will remain as small as possible.

After the heating body 11 has been heated up to the desired temperature, the heating body 44 above the test body is tilted outwardly, and the shearing strength of the test body 11 is measured by means of a suitable, for instance hydraulic, shearing strength testing device. The testing device diagrammatically illustrated in the drawing is connected to a stand 16. Stand 16, in its turn is firmly connected to the bottom plate 12 by means of screws 37.

The testing device proper consists of two parts detachable from each other. One of said parts contains the pressure cylinder 31, whereas the other part contains the working cylinder 22. The sleeve 17 containing the working cylinder 22 is provided with a thread 18 which threadedly engages a corresponding threaded bore in stand 16.

Displaceably arranged in the working cylinder 22 is a piston 33 having connected thereto a piston rod 34. Piston rod 34 passes through a bore 21 of a closing plate connected to sleeve 17. The end of piston rod 34 has connected thereto a plate which, for better guiding ring 6, is provided with a guiding path 46 (FIG. 4) in conformity with the outer diameter of the ring. On that side which is located opposite the closure plate 20 there is provided a threaded bore arranged coaxially with regard to the working cylinder 22. The threaded bore is engaged by a sleeve 25 with the corresponding thread 23 while a sealing ring or gasket 38 is interposed between sleeve 25 and sleeve 17. Sleeve 25 confines a pressure cylinder 31 which, through a bore 32, communicates with the cylinder 22. Displaceably arranged in cylinder 31 is a pressure piston 3t) which is adapted to be actuated by means of a hand wheel 28 on one end of a spindle 27 having its other end connected to piston 30. Spindle 27 is provided with a thread 29 threadedly engaging the closure plate 26 connected to sleeve 25. Advantageously, the surface of pressure piston 30 is five times greater than the surface of piston 33 in order to be able better to measure by means of a pressure gauge 36 the forces required for shearing the hard crust off the test body 11. In order to save time-consuming conversions, the scale of the pressure gauge 36 has been so designed that there can be read on the same the pressure exerted upon ring 6 and also the pressure exerted by the pressure piston 30.

Attention is directed to the fact that in conformity with the requirements, sleeve 17 may be replaced by another sleeve confining a larger or smaller diameter cylinder.

As will be evident from the above, the method according to the present invention makes it possible, in a simple manner, to ascertain the shearing strength of the bordering layer when a hard crust is formed in the sand.

It is, of course, to be understood that the present invention is, by no means, limited to the particular construction and method set forth above, but also comprises any modifications within the scope of the appended claims.

What we claim is:

1. In an apparatus for use in connection with a test body made up of foundry sand to be investigated and comprising an annular member confining an end layer of said test body, which includes: holding means forming a chamber for receiving and holding said test body while leaving a portion thereof projecting from the holding means disposed in said annular member with the end surface layer thereof exposed, heating means movable selectively into close relationship with said exposed end surface of said test body for subjecting said end surface to sudden heat of at least 1067 F. for a selected time to create a crust on the test body confined by said annular member and relatively hard with regard to the remainder of the foundry sand making up said test body, power operable means operable to engage and move said annular member in its own plane and in a direction lateral to the test body so as to shear off the portion of the test body within said annular member from the remainder of said test body, and force-responsive means operatively connected to said power operable means for measuring the force required for said shearing-off operation.

2. In an apparatus for ascertaining the border layer strength below the surface of unilaterally highly heated compacted foundry sand, which includes: tubular holding means for receiving therein and holding a test body made up of the foundry sand to be investigated with a portion of the test body projecting upwardly from the tubular holding means, ring meanssurrounding said projecting portion and leaving exposed an end surface of said projecting portion of said test body when the latter is received by said holding means, heating means having a heating surface substantially transverse to the axis of said tubular holding means and movable selectively into substantially axial alignment with said tubular holding means and close to one end thereof above said ring so as to be inheat transfer relation tosaid end surface of said projecting portion of the test body, and power operable means arranged at the level of said ring means and movable transverse to the longitudinal axis of said tubular holding means and operable for moving at least an axial portion of said ring laterally of said holding means for 5 6 shearing-oif the said projecting portion of the test body References Cited by the Examiner received in said holding means, and means operatively UNITED STATES PATENTS connected to said power operable means for indicating the force exerted on said ring means during said shearing. 2,491,512 12/1949 Moore 3. An apparatus according to claim 2 in which said 5 2,660,051 11/1953 Dowling 7315.6

ring means comprises a first ring extending partly into said tubular holding means and thus held stationary thereby, RICHARD QUEISSER, Examine"- and a second ring resting on said first ring and forming DAVID SCHONBERG, Examiner that portion of said ring means Which is moved by said power operable means. 10 I C. GOLDSTEIN, Assistant Examiner. 

1. IN AN APPARATUS FOR USE IN CONNECTION WITH A TEST BODY MADE UP OF FOUNDRY SAID TO BE INVESTIGATED AND COMPRISING AN ANNULAR MEMBER CONFINING AN END LAYER OF SAID TEST BODY, WHICH INCLUDES: HOLDING MEANS FORMING A CHAMBER FOR RECEIVING AND HOLDING SAID TEST BODY WHILE LEAVING A PORTION THEREOF PROJECTING FROM THE HOLDING MEANS DISPOSED IN SAID ANNULAR MEMBER WITH THE END SURFACE LAYER THEEOF EXPOSED, HEATING MEANS MOVABLE SELECTIVELY INTO CLOSE RELATIONSHIP WITH SAID EXPOSED END SURFACE OF SAID TEST BODY FOR SUBJECTING SAID END SURFACE TO SUDDEN HEAR OF AT LEAST 1067*F. FOR A SELECTED TIME TO CREATE A CRUST ON THE TEST BODY CONFINED BY SAID ANNULAR MEMBER AND RELATIVELY HARD WITH REGARD TO THE REMAINDER OF THE FOUNDARY SANK MAKING UP SAID TEST BODY, POWER OPERABLE MEAND OPERABLE TO ENGAGE AND MOVE SAID ANNULAR MEMBER IN ITS OWN PLANE AND IN A DIRECTION LATERAL TO THE TEST BODY SO AS TO SHEAR OFF THE PORTION OF THE TEST BODY WITHIN SAID ANNULAR MEMBER FROM THE REMAINDER OF SAID TEST BODY, AND FORCE-REPONSIVE MEANS FOR MEASURING CONNECTED TO SAID POWER OPERABLE MEANS FOR MEASURING THE FORCE REQUIRED FOR SAID SHEARING-OFF OPERATION. 